Combustion control system



Jan. 21, 1941. c. H. SMITH 2,229,350

COMBUSTION CONTROL SYSTEM Filed Jan. 5, 1940 2 Sheets-Sheet 1 INVENTORCHARLES H SMITH ATTORNEY Jan. 21, 1941. rr 2,229,350

COMBUSTION CONTROL SYSTEM Filed Jan. 5, 1940 2 Sheets-Sheet 2 Ia/[00266205 r25 J JW/Tcl/ R 1 48 Z4 33 30$ curour SWITCH 28.4 (THERMALomezmp) ZZ O FROM STEAM LINE FROM BOILER WATL-kf INVENTOR CHAR]. 5.5 H.SMITH BY W A RNEY Patented Jan. 21, 1941 UNI ED s'i'A'ras miss;

cosmos-non comer. srs'rnsr car... 1!. Smith, Newark, N. 1., alaignor to1.. .r.

Wing Mfg. 00., New York N. Y., a corporation of New York ApplicationJanuary 5, 190, serial No. 312,48

11 cum (01. 110-54) The present invention relates to 'a system ofcombustion control for low pressure heating boilers using solid fuel andto the apparatus forming part of said system.

Perhaps the greatest inconveniencein the use of solid fuel boilers isthe necessity for frequent attendance thereof. This is especially truewhen low pressure heatingboilers are fired with the cheaper grades ofcoal, suchas buckwheat, bar- 10 ley and rice. When using such grades ofcoal, particularly rice coal, low grade bituminous, briquettes and thelike, which require forced draft blowers for their proper combustion, itis necessary to stroke the boiler frequently, sometimes as 15 often asevery one half hour or less.

The heating industry has, therefore, been seek-' ing some method ofoperating boilers which would require less labor and attention and stillpermit the use of these cheaper grades of coal.

20 The present invention contemplates the provision of a system which isdesigned to utilize the cheaper as well as the better grades of coal,and yet which requires comparatively little attention. In ordinarycommercial installation, 25 such as those furnishing heating service toapartment houses, oifioes, schools, hospitals, institu-.

tions and industrial structures, the present system has been found to becapable of completely automatic operation for periods of twenty-four 30and even forty-eight hours in extreme weather with heavy loads'. Underlight loads, such as the, supplying of summer hot water, one firing perweek has been found adequate. The value of the present system can beappreciated when com- 35 parison of the above figures is made with therequirements of the ordinary commercial installa-' tion which requires'stoking several times daily and oftentimes one half hourly.

Furthermore, since my system does not re- 40 quire the use of high gradecoal, although it is capable of utilizing the same with attendantadvantages, a considerable economy in heating costs results from itsuse.

In most commercial buildings, heat is turned 45 of! during thenight andthe fire in the boiler is banked. Therefore, with the conventionalsystems now employed, in changing from nighttime to daytime heating, aheavy load is put on the heating system to reheat the furnace, the water50 in the boiler, the risers, and'the pipes which have become coldduring the night.

With the system of the present invention. the.

fire is not banked in the boiler but is operated to maintain a watertemperature in the boiler just 55 below the boiling point. Thus, duringthe night,

the furnace is maintained at a minimum temperature which assures ,thewater return, the steam pipes, and the heating system in general beingkept warm. a

With the present system of control, therefore, 5 the heavy morningreheating load is eliminated.

Furthermore, water hammer which usually occurs in the morning when coldpipes are reheated is reduced o'reliminated. The entire building inwhich the system of the present invention is installed is kept at amoresteady and comfortable building temperature. a

It is recognized'that boilers are heated .by (a) conductionof the heatof the gases of combustion, and (b) radiation of heat from an intensefireof the fuel bed, the latter requiring high rates of fuel combustionper unit of grate area.

In the conventional system, extremely high rates of heat transfer arerequired to meet the demands of the sudden and extreme changes of theheating load, such as are encountered in the early morning. In suchconventional systems, reliance must, therefore, be placed largely uponradiant heat requiring an extremely ,hi h rate of fuel combustionattendant with high fuel bed fire intensity.

With, the cheaper grades of 'fuel and the con-- ventional system, arelatively thin fuel bed must be provided in order-to present theradiant heat of the fire directly to the boiler heating surfaces and toprevent the formation of clinker ,in the- .fuel bed.

The present system of control, on the other hand, is arranged to operatelargely by conduction rather than by radiation, thereby reducing therate of fuel combustion and the number of stokingsrequired andeliminating the formation of clinker. The efilciency of the entiresystem is thereby increased, reducing, in addition, fuel consumption. 40

Further and other advantages and objects of the present invention willbe apparent fromthe following description and the drawings in connectiontherewith, in' which Fig. 1 is a schematic diagram of a steam boiler, acontrol board panel, and connections between said boiler and controlboard panel, which embody the present invention.

Fig. 2 is a schematic diagram of the control board panel shown in Fig.1.

conventional heating plant possesses reserve capacity in order to meetthe peak heating requirements, such as when changing from night to dayheating. A low pressure steam heating boiler is used in the illustrationof my invention, though it will be understood that my invention may beapplied to other heating boilers, such as the water or vapor type orboilers of high operating pressure.

Unlike the conventional systems, which require that the boiler be stokedfrequently with thin layers of coal arranged on the bed, with thepresent system, the boiler III is required to be fired not morefrequently than once every twenty-four hours. Instead of a thin layer ofcoal, however, the boiler i0 is filled to the top, the coal above theburning area being utilized as reserve fuel and automatically fed bymeans of gravity to the bed. I, therefore, utilize the relatively amplespace found above the conventional boiler. This type of stoking is notpossible with systems which depend for their heating upon the radiantenergy from the fire bed, but is possible with the present systemwhichis adapted to operate upon conduction of the heat by the gases generatedduring combustion.

After the boiler l0 has been stoked, the combustion of fuel isautomatically maintained during the day to provide, within selectedlimits of steam pressure, the quantity of steam required for the heatingload. At night, it is automatically adjusted so as to produce atemperature just below the boiling point, such as between to 200Fahrenheit. Thus, the water in the boiler and the pipes leading theretoare kept warm throughout the night and consequently the usual morningload required to change from night to day heating is reduced oreliminated. This results in a saving of fuel and provides a more steadyand comfortable building temperature. There is no abrupt drop in roomtemperature at night as occurs in the usual system when the fire in theboiler is damped.

With the cheaper grades of coal, the ordinary draft from the chimney isnot adequate to provide proper combustion. Therefore, in order to adaptthe boiler ID to use the cheaper grades of coal, I provide a forceddraft blower l2 driven by an electric motor M or some similar means ofpower. When the coal in the boiler I0 is to be burned rapidly, the motorl4 and the blower I 2 are operated. When, however, the coal in theboiler is to be burned at a slower rate, the motor is shut off andcombustion is then maintained by the chiinney draft.

In order that the fuel bed may have an ample supply of air, underinfluence of the chimney draft, when the blower is not in operation, Iprefer to use a propeller type of blower, the casing l3 and ashpit ductl5 of which, for practical purposes, present a substantially unimpededpassage, though it will be understood that other suitable forced draftmeans may be provided.

The present system is provided with a pressurestat which willautomatically cause operation of the motor I4 and blower l2 when thepressure in the boiler falls below a preselected magnitude, therebyincreasing the rate of combustion and raising the boiler pressure to theselected magnitude, when operation of the blower motor is automaticallystopped.

Sometimes, however, even though the blower is no longer operating thechimney draft itself may be sufiicientto cause the boiler pressure tofur to be completely closed before the motor begins to operate; asotherwise, the blower would force the gases of combustion through theopen check into 'the boiler room. The check draft damper l6 illustratedis preferably of the gravity closing type and mechanisms for opening andclosing it in the manner hereinbefore set forth will be describedhereinafter.

The various instruments for controlling the operation of the boiler l0through control of the motor l4 and blower i2 and the check draft damperl6 are preferably located adjacent the boiler on a control board panel20.

In order to operate the motor l4, it is connected to a suitableavailable source of current supply.

Lines 22 from a suitable electric power supply source may be brought toa conventional splice box 24 mounted on the control panel 20. From thesplice box 24, the main power supply is connected to the customary mainline fused safety switch 26 of the double pole, manually operated type.In turn, one lead from the main switch may be connected in series .withone side 28 of a cutout switch (thermal overload) 36 through the splicebox 24 to one terminal 32 of the motor I4. The other lead from the mainswitch 26 is connected in series with a manually operable variablerheostat 34, a tiltably-operated mercoid switch 36 and the other side 38of the cutout switch 28 through the splice box 24 to the second terminal40 of motor M. It will be seen that, when the main line switch 26, thecutout switch 30 and the mercoid switch 36 are all closed, current willbe supplied to drive the motor I4, the amount of current supplied beingcontrolled by varying the rheostat 34. The speed of the motor i4 isvaried by the rheostat, thereby controlling, as desired, the quantityand pressure of the air supplied to the ashpit.

Under ordinary operating conditions, the main line fused switch 26 iskept closed and is only opened when repairs are to be made or the fusesin such switch are to be changed. The fuses in this switch serve theirnormal function of preventing injury to the apparatus due to excesscurrent or injury to the main line due to a short circuit in theapparatus. The construction of the main line switch 26 is well knownand, therefore, need not be described. The function of the cutout switch30 is to protect the forced draft blower motor l4 from current overload.It may be of any suitable construction, the one herein described beingthermally operated so that when more than the fixed amount of currentpasses through said switch, the excess heat produced will cause suchswitch to open. The cutout switch 30 is also ordinarily closed. Sincethe construction of such switches is well known, the details thereofneed not be described.

The blower motor circuit is provided with a switch 36, preferably of theconventional mercury tube type, a well known example of which is the"Mercoid switch. The operation of this switch is controlled, as willhereinafter be described, by

' erate the blower motor.

ams'ud a pressurest'at or aquastat to thereby suitably opoperation ofsuch mercury tube switches being well known, it is not necessary todescribe its specific structure.

Such switch is adapted to be opened or closed by being tilted anddepends for its operation on a drop of mercury being moved, by tilting,in position to touch the switch. The operation of this switch 88, whichwill be more fully described, is dependent upon the steam pressure orwater temperature created by combustion in the boiler, being arranged toautomatically close when the pressure or temperature in the boiler fallsbelow a selected magnitude and open when it is raised to said selectedmagnitude.

After a boiler has been stoked and the temper-.- ature of the coal inthe boiler is initially raised, a large quantity of combustible gasesare given of! by the coal. For reasons of safety. it is necessary,therefore, that these gases be completely burned before operation of theblower is stopped.

It will be apparent, should the blower operation cease under automaticcontrol before such combustible gases are consumed, they will form alayer at the top of the coal bed. This comparatively large amount ofunconsumed gas, when operation of the blower is again commenced, maybecome ignited by the resulting hot gases of combustion or by coming incontact with live coals in the flre bed, possibly resulting in anexplosion.

For this reason, regardless of the pressure in the boiler, it isnecessary to maintain the blowers in operation for a fixed period afterany stoking to consume these gases. This period is usually from fifteento thlrtyminutes.

To maintain the blowers in operation for this fixed period, I prefer toprovide a time ignition switch 42. The time ignition switch 42 isconnected in parallel with the mercoid switch 88. The time ignitionswitch 42 is manually closed after stoking and automatically will stayclosed for a fixed period at the end of which period it willautomatically open. It will be seen that when the time ignition switch42 is closed current will be supplied to the motor l4 and that theblower I! will operate to consume whatever combustible gases remain inthe combustion chamber or furnace of the boiler. The specificconstruction of such time ignition switch is well known and, therefore,need not be described.

It is, of course. to be understood that in place of the time ignitionswitch 42 a simple manually operated switch might be employed whichwould be closed by the stoker of the boiler and opened by him after. afixed period has passed. However, since the use -'of'such manuallyoperated switch would require the attention of the stoker and wouldresult in a considerable waste of his time, as well as the danger of hisforgetting to open the switch, it is preferred that the automaticallyopening time ignition switch 42 be employed.

It will be apparent that when the time ignition switch 42 is opened, theoperative opening and closing of the blower motor circuit will becontrolled by the mercury tube switch 88, which, in

cooperation with, the check draft damper l4, controls the pressure atwhich the. boiler is operated. The means for controlling this checkdraft damper will be hereinafter described.

In the present system, it is intended to operate the boiler. under twodifferent automatic .oper- The construction andtwo poles or contacts ofsaid sting conditions, one required for daytime heating and the otherrequired for nighttime heating. During the day, as heretofore stated,the boiler fuel combustion is controlled by a pressurestat, whichmaintains the desired boiler steam pressure. During the night, boilerfuel consumption is controlled, as hereinafter described, by anaquastat, to maintain the desired boiler water temperature.

To accomplish this, I provide two separate means for controlling boththe mercury tube switch 84 and the check draft damper, one for daytimeuse and the other for nighttime use. While manual means might beemployed to shift from 'the daytime control to the nighttime control, itis preferred that automatic means be utilized in order that no attentionthereto will be required.

For this purpose, I first provide a conventional time switch whichcomprises a schedule clock 44, adapted to maintain the switch 48 closedfor a selected period of time and then open it for another selectedperiodbefore closing it again. Inasmuch as the construction of such timeswitch is well known, it will not be here described. In the presentembodiment of my invention, the schedule clock is arranged to close theswitch 48 during the day and to open it at night. In the arrangementillustrated in Figure 2, I have shown the clock mechanism of theschedule clock connected to the main power supply through a fuse block48, which fuse block is intended to prevent injury to the windings ofthe schedule clock.

The switch 48 of the schedule clock is arranged to open and close acircuit in a day-night changeover relay 88.

The relay '8 has a solenoid 82' having one lead therefrom connecteddirectly to one leg of the main line fused switch 28 and the other leadconnected to the other leg of the main line fused switch through the,schedule clock switch 48.

when the schedule clock switch 48 is closed, current will flow throughthe solenoid 52. This will attract and further draw in a movable ironcore 84 arranged partly within the solenoid. Two

movable contacts 88, insulated from each other,

are arranged on, and adapted to move with, said movable iron core 84 andto make contact with two upper stationary poles 58. The upper stationarypoles 88 are connected to the daytime control for the mercury tube andcheck draft damper. It will be seen that, when the schedule clock switch48 opens, current will no longer flow that by moving these contacts sothat they touch the stationary poles 88 or the stationary poles 88either .the daytime or the nighttime control instruments will govern theoperation of the mercury tube switch and the check draft damper.

It is, of course, to be understood that in place of the schedule clockand the day-night changeover relay l4 manually-operated means, such asthe usual double pole, double throw switch, might be employed. However,the automatic means above described are preferred.

However, whenever it may become desirable to operate the boiler undernighttime control conditions continuously at any time, for example inthe early fall or late spring, when the heating load is extremely light,or in the summer time, when the heating boiler is used, with well knownapparatus, such as submerged heaters, to operate a hot water boiler, Ihave provided a manual switch 62, the one illustrated being of thetoggle variety in series with the schedule clock switch 48. This switch62 may be manually opened to thereby open the schedule clock switchcircuit, so that no current will pass through the solenoid and themovable contacts 56 will, therefore, be kept continually in contact withthe stationary poles 60 to thereby maintain the nighttime controls incontrol of the operation of the boiler.

It will, of course, be understood that when it is desired to operate theboiler continuously under daytime conditions, the schedule clock may bearranged to continuously maintain closed the switch 48 for the desiredperiod of operation.

Ordinarily, however, the switch 62 is kept closed and the schedule clockautomatically changes from daytime to nighttime operating temperaturesand pressures.

The remaining instruments to be described are control instruments andare adapted to be operated with a voltage lower than that supplied bythe power supply line 22. In order to obtain this lower voltage, Iprovide a step-down transformer 64. The primary of the step-downtransformer 64 is connected to the main line fused switch 26. Thesecondary is connected to the ,various control instruments in a mannerthat will be hereinafter described.

To provide for daytime control of the boiler, I prefer to arrange on thecontrol board panel 20 a modulating steam pressure regulator(pressurestat) 66, and to provide for nighttime control I arrange amodulating vapor pressure regulator (aquastat) 68 on the same panel. Thesteam pressure regulator 66 is connected by a pipe II of comparativelysmall diameter to the steam header III of the boiler. This pipe enters asensitive bellows 12 arranged in the steam pressure regulator. Thebellows 72 are adapted to be extended when the pressure in the mainheader I0 rises and to contract when the pressure in the main header I0falls. To the end of the bellows I2, I connect the movable arm 14 of apotentiometer 16. It will be apparent that this arm 14 will move acrossthe potentiometer in relation to the rising or falling of pressure inthe steam header 10. The ends of the resistance 18 of the potentiometer16 are connected .to the upper stationary poles 58 of the change-overrelay 50,

and, when the movable contacts 56 of the relay plied to a single boiler,it will be understood that it may be applied to a battery of two or moreboilers, each of which is connected to one or more blowers. In suchcase, the pipe II is connected to the common steam header.

The modulating water or vapor temperature regulator 68, which is aconventional aquastat, is intended for nighttime control and isarranged, therefore, to be operated by the boiler water temperature orby boiler vapor temperature. I prefer, therefore, to connect thisaquastat by means of a pipe of comparatively small diameter to a bulb 89arranged in the-boiler just below or just above the hot water line. Thispipe is connected in the modulating vapor temperature regulator 60 to asensitive bellows 80. Any suitable gas is sealed in the bulb 80, thebellows and the pipe connecting the change in the temperature of thewater or the vapor just above the water line will effect correspondingmovement of the bellows 00, thereby providinga relatively sensitiveinstrument for nighttime control. Where two or more boilers are to beused, the bulb is arranged in such place where it will be controlled bythe temperature common to all. The movable arm 82 of a potentiometer 84is arranged on the moving end of the bellows '80 and, therefore, willmove in accordance with the temperature of the water in the water coilsin the boiler. The two ends of the resistance 88 of the potentiometer 84are connected to the lower stationary poles 00 of the change-over relay50 and-the resistance 88 is adapted to be arrangedinto the controlcircuit when the moving contacts 50 are in touch with the lowerstationary poles 80.

It will, therefore, be apparent that the change-' over relay 50, whichis controlled by the schedule clock 44, will bring either the modulatingsteam pressure regulator 68 or the modulating vapor temperatureregulator 88 into the control circuit to control the "operation of theboiler during the day or during the night.

I have already described how the movement of the potentiometer arm I4and the movement of the potentiometer arm 82 are controlled respectivelyby the steam pressure or vapor or water temperature in the boiler. Iwill now describe how these movements in turn affect the closing of themercury tube blower switch and the opening of the check damper I8.

For the purpose of simplifying the following explanation, I assume thatthe apparatus is set for daytime operation as illustrated in Fig. 2 andthat the resistance I8 has both ends thereof connected to the upperstationary poles 58 and that the change-over relay 50 has its movablecontacts 56 arranged in contact with the upper stationary poles 58.

It will be seen that one end 88 of resistance I8 of the potentiometer I6is connected through the change-over relay 50 and through a coil I00 toone end 98 of a resistance 94, both of the latter forming part of amodulating electric compensator 91. The resistance 94 is part of apotentiometer 96. The other end 92 of the resistance 94 is in turnconnected back through the coil and the change-over relay 50 to theother end I02 of the resistance 18. It will be seen, therefore, thatresistance 18, coil 90, resistance 94 and coil I 00 are all arranged inseries in a closed circuit which comes back to resistance 18.

Arm I4 of potentiometer 16 may be then connected to one end of thesecondary of the stepdown transformer 84 and the other end of thesecondary of the step-down transformer 84 is connected to the arm I04 ofthe potentiometer 96. It will be seen that the current will flow betweenthe two arms through the resistances and will be divided through thecoils 90 and I00. It will furthermore be apparent that by adjusting thepotentiometer arms the current flowing in coils 90 and I 00 may be madeequal. After the currents in coils 90 and I00 are equal, if the arm I4is moved, due to the movement of the bellows I2 caused by achange in thepressure in the steam line, the amount of current flowing through coils90 and I00 will be changed and more current will flow through one coilthan the other.

' The coils 66 and I66 form part of a pendulum type of switch I66. Theswitch I66 consists of an inverted U- ped soft iron core I66 having itstwo legs partially arranged within coils 66 and Ill, respectively, saidcore I66 being pivoted at the center thereof. A contact arm III is ar-'iron core arranged therein than is exerted on the is: arranged withinthe coil Ill and thus the soft iron core will tilt, thereby tilting thecontact arm III! and cause it to make contact with the fixed pole II2.Conversely, when there is greater current passing through coil III thetiltable contact arm will tilt to the right and make contact with thefixed pole Ill.

The tiltable contact arm H6 is connected to one end III of the secondarystep-down transformer 64, the other end III of the step-down transformer64 being connected to the common terminal of a conventional reversiblemotor 4. The construction of such motors being well known, motor I I4will not be here described. The two poles H2 and H3 of the pendulum typeswitch I66 are connected to the reversible motor II 4. These poles areso connected with the motor coils of motor I I4 that when the tiltablearm II6 touches the fixed pole II2 it drives the motor in one direction,and when it touches the fixed pole II6 it drives the motor in theopposite direction. In the embodiment illustrated, I ,prefer to arrangethe motor II 4 so that when the tiltable contact arm III) touches thefixed pole III the shaft II6 of the reversible motor II4 will turn in acounterclockwise direction, as shown in the drawings, and when thetiltable contact arm touches the fixed pole I I2 the shaft will turn ina clockwise direction.

The shaft II6 of the reversible motor 4 is connected to the movable armI64 of potentiometer 66 by any suitable arrangement such as the crankand link II6. Thus,- when the motor moves, the potentiometer arm willmove over the resistance 94. On the same shaft II6, I arrange a long armI26, on one end of which'I arrange the mercury tube switch 66. The otherend of said arm I26 is connected by any suitable means such as a cable,chain, cr rope I22 over pulleys I24 and I26 to the check draft damperI6.

The operation of the control device will now be described.

Let us assume that the motor I4 is operating the blower I2 and therebyraising the pressure within the boiler. That is the conditionillustrated in Fig. 2 where the globule of mercury in the mercury tube36 is shown connecting the two contact points in 'such switch therebyclosing the motor circuit. As the pressure in the steam header I6 beginsto rise, the bellows 12 in the modulating steam pressure regulator 66begin to expand, moving the potentiometer arm I4 to the right. As aresult, the current in the potentiometer circuit is unbalanced andgreater current flows through coil 66 than flows through coil I06. Thetiltable contact arm IIII tilts and touches the fixed pole II2 therebycausing the shaft II6 of the motor I I4 to move in a counterclockwisedirection. when the motor moves in a counterclockwise direction, itrotates the long arm I26 in a counterclockwise direction.

It also moves the potentiometer arm- I64 toward the left. The movementof the potentiometer arm toward the left will increase .the amount ofcurrent flowing through coil I66 and when the amount of current in coilIII is equal to the amountmf current in coil 66 the tiltable contact armII6 will be moved away from the fixed poles II! and will remain-be-'tween the fixed poles. As soon as the tiltable arm moves away from thefixed pole III, the motor will cease to operate and the shaft I I6 willstop turning. Since the currents in 66 and Ill are then equal, thepotentiometer arms will stay fixed until further movement of the bellows12, to again unbalance, the amount of current passing through coils 66and I66.

It will be observed that when the shaft II6 moves in a counterclockwisedirection to thereby balance the current flowing through coils 66 andI66, the long arm I26 also moves counterclock wise. The mercury in themercury tube. switch moves away from the two contacts to thereby openthe mercury tube switch upon the initial counterclockwisemovement of thelong arm I26. The further counterclockwise movement of the. long arm I26pulls the chain I22 which is connected with one end of the long arm I26and opens the check damper I6.

To summarize this operation, it will be seen that when the pressure inthe boiler increased, the controlapparatus caused the mercury tubeswitch first to be opened and further increase of pressure in the boilerand, therefore, in the bellows 12 caused the check damper to open. It ismost important to note that the opening of the damper is not abrupt, butthat the damper opens Y more and more as the pressure rises.

After the motor has been shut off and the check draft damper openedacertain distance, the pressure in the boiler may start to fall. When thepressure in the boiler starts to fall, the bellows 12 will contract,moving the potentiometer arm 14 toward the end 66 of the resistance 16.This will in turn cause greater current to flow I through coil I66, tothereby tilt the tiltable contact arm III to make contact with the fixedpole III and thereby cause /the reversible motor I I4 to be rotated in aclockwise direction. Again, the potentiometer arm I64 will be moved in adirection to increase the current in coil 66 until the current in thecoils 66 and I06 are balanced. At the same time, the arm I26 will berotated clockwise, thereby releasing tension on the chain I22 connectingit to the'check damper and allowing the check damper to close, and then,only after the check damper has been completely closed, will the globuleof mercury in the mercury tube switch 36 close the contact therein.

From theforegoing description, the operation of the modulating vaportemperature regulator will readily be understood when it is shifted intoplace of the modulating steam pressure regulator by the action of theschedule clock 44. The potentiometer arm 62 of the modulating vaportemperature regulator 66 is electrically connected to the potentiometer14 of the modulating steam pressure regulator 66 The potentiometerrelater by the mere operation of the daytimenighttime change-over relay50 are substituted in the control circuits in place of each other andoperate similarly except that they operate at different temperatures andpressures.

It is to be understood that the predetermined pressure or temperature atwhich the boiler operates may be changed by adjusting either of thebellows .or the positions of the potentiometer arms with respect totheir bellows. Other means of adjusting this predetermined pressure ortemperature will readily occur to one versed in the art and will,therefore, not be described.

' To recapitulate, it will be apparent that by the arrangement of theautomatic controls illustrated, I have eliminated the necessity ofperiodic high rates of fuel combustion per unit of boiler grate surfaceheretofore required with other systems and methods of control. With thesystem described, the combustion of fuel is enabled to take place in thefuel bed and the relatively ample space above the fire-zone, provided inall conventional boilers, may, therefore, be used for the storage offresh fuel not possible wtthconventional systems and methods of controlheretofore used with the cheaper and smaller grades of coal such asanthracite, buckwheat, rice, barley, bituminous slack, waste fuels andthe like.

These results are in short accomplished by utilizing, under the propercontrol described, in combination forced draft and natural chimneydraft, there being no control of the latter except the automatic checkdraft described. Such controls are the pressurestat and aquastat forautomatically and continuously maintaining the boiler at the selectedoperating conditions, the time clock switch for automatically changingfrom daytime to nighttime operating conditions and back again and thetime switch to eliminate the possibility of explosion of unburned gasesafter stoking.

While I have described the construction and operation of the presentsystem and its apparatus in particular detail, I do not wish to belimited to the specific details herein set forth, but intend to claimthe invention as broadly as the state of the prior art and the scope ofthe appended claims permit. Accordingly, while I have described theapparatus as adapted to operate only a single forced draft blower and asingle check draft damper, the system and apparatus herein described canbe readily adapted to operate several blowers, several dampers and,therefore, several different boiler units.

I claim:

1. A combustion control system for a boiler having a breeching andburning solid fuel comprising, in combination, a motor driven bloweroperatively connected to said boiler, a check draft damper arranged inthe breeching, an electric circuit for said blower motor, a switcharranged in said blower circuit and adapted to open and close saidblower circuit, electromagnetic means operatively connected to both thedamper and the switch for opening and closing said switch and saiddamper, pressure controlled means responsive to the steam pressure insaid boiler for operating the electromagnetic means, temperaturecontrolled means responsive to the temperature of the boiler water orboiler vapor for operating the electromagnetic means, a relay connectedto the pressure controlled means, temperature controlled means and theelectromagnetic means, said relay being adapted to operatively connecteither the pressure controlled means or the temperature controlled meanstothe electromagnetic means, a circuit for operating said change-overrelay, a time schedule switch arranged in the relay circuit and adaptedto control said relay.

2. A combustion control system for a boiler having a breeching andburning solid fuel comprising, in combination, a motor driven bloweroperatively connected tosaid boiler, a check draft damper arranged inthe breeching,'an'electric circuit for said blower motor, a switcharranged in said blower circuit and adapted to open and close saidblower circuit, electromagnetic means operatively connected to both the.

damper and the switch for opening and closing said switch and saiddamper, pressure controlled means responsive to the steam pressure insaid boiler for operating the electromagnetic means, temperaturecontrolled means responsive to the temperature of'the boiler water orboiler vapor for operating the electromagnetic means, a relay connectedto the pressure controlled means, temperature controlled means and theelectromagnetic means, said relay being adapted to operatively connecteither the pressure controlled means or the temperature controlled meansto the electromagnetic means, a circuit for operating said change-overrelay, a switch arranged in the relay circuit and adapted to controlsaid relay.

3. In a combustion control system for a boiler having a breeching andburning solid fuel, in combination, a check draft damper arranged in thebreeching, electromagnetic means operatively connected to the damper foropening and closing said damper, pressure controlled means responsive tothe steam pressure in said boiler for operating the electromagneticmeans, temperature controlled means responsive to the tempera ture ofthe boiler water or boiler vapor for operating the electromagneticmeans, a relay connected to the. pressure controlled means, temperaturecontrolled means and the electromagnetic means, said relay being adaptedto operatively connect either the pressure controlled means or thetemperature controlled means to the electromagnetic means, a circuit foroperating said relay, a time schedule switch arranged in the relaycircuit and adapted to control said relay.

.4. In a combustion control system for a boiler having a breeching andburning solid fuel, in combination, a check draft damper arranged in thebreeching, electromagnetic means operatively connected to the damper foropening and closing said damper, pressure controlled means responsive tothe steam pressure in said boiler for operating the electromagneticmeans, temperature controlled means responsive to the temperature of theboiler water or boiler vapor for operating the electromagnetic means, arelay connected to the pressure controlled means, temperature controlledmeans and the electromagnetic means, said relay being adapted tooperatively connect either the pressure controlled means or thetemperature controlled means to the electromagnetic means, a circuit foroperating said relay, a switch arranged in the relay circuit and adaptedto control said relay.

5. A combustion control system for a boiler having a breeching andburning solid fuel comprising in combination a motor driven bloweroperatively connected to said boiler, a check draft damper arranged inthe breeching, an electric circuit for said blower motor, a switcharranged in said circuit and adapted to open and close said s,aao,aso iP switch movement controlling means being opercircuit, a reversibleelectrical motor having a rotatable shaft, an arm arranged on saidreversible motor shaft operatively connected to the switch in the blowermotor circuit and to the check draft damper, means controlled by thepressure in theboiler for operating the reversible motor, said meansbeing adapted to turn the reversible motor shaft in one direction whenthe pressure in the boiler increases and in theopposite direction whenthe pressure decreases.

'6. A combustion control system for a boiler having a breeching andburning solid fuel comprising, in combination, a motor driven'bloweroperatively connected to said boiler, a check draft damper arranged inthe breeching, an electric circuit for said blower motor, a tiltablyoperated mercury tube switch arranged in said circuit and adapted toopen and close the circuit, a control device for said mercury tubeswitch and said check draft damper comprising a reversible motor havinga shaft, an .arm arranged intermediate its ends on said shaft and having.one end thereof operatively connected to the check draft-damper, theother end thereof having the mercury tube switch arranged thereon, anelectric circuit for said reversible motor, a movable switchfor-controlling the direction of rotation of the motor,

means for controlling movement of said switch,-

a pair of potentiometers having their resistances connected in parallel,the switch movement controlling means being operatively connected tosaid resistances, the arms of the potentiometers being connected to asource of current, the arm mercury tube switch arranged in said motorcircuit and adapted to open and close said circuit, a pivoted arm havingone end thereof connected to the check draft damper and having themercury tube arranged on the other end thereof, means controlled by thepressure in said boiler for tilting said arm, said pivoted arm, checkdraft damper and mercury tube being arranged relatively to each other sothat upon tilting of the arm in a direction to open said check draftdamper, the mercury tube switch is first opened before the initialopening movement of the check draft damper.

8. A combustion control system for a boiler having a breeching andburning solid fuel comprising, in combination, a motor driven bloweroperatively connected to said boiler, a check draft damper arranged inthe breeching, an electric circuit for said blower motor, a tiltablyoperated mercury tube switch arranged in said circuit and adapted toopen and close the circuit, a control device for said mercury tubeswitch and said check draft damper comprising a' reversible motor havinga shaft operatively connected to the check draft damper and the blowermotor switch, an electric circuit for said reversible motor, a movableswitch for controlling the direction of rotation of the motor, means forcontrolling movement of said switch, a pair of potentiometers havingtheir resistances connected in parallel, the

1 having a breeching and burning solid fuel comprising, in combination,amotor driven blower atively' connected to said resistances, the arms ofthe P t ntiometers being connected to a source of current, the arm ofone-of said potentiometers" being movably connected with the motorshaft, 6 means responsive to boiler conditions for moving the arm of theother potentiometer.

9. A. combustion control system .for .a boiler 10 operatively connectedto said boiler, a check draft damper arranged in the breeching,-anelectric circuit for said blower motor, a blower motor switch arrangedin said circuit and adapted to open .and. close the circuit, a controldevice for 15 said blower motor switch and said check draft dampercomprising a reversible motor having a shaft, an arm arrangedintermediate its ends of said shaftand having one end thereofoperatively connected to the check-draft damper, the other 20 endthereof being operatively connected to the blower motor switch, anelectric circuit for said reversible motor, a movable switch forcontrolling the direction of rotation of the motor, means forcontrolling movement of said switch, a pair of potentiometers havingtheir resistances oonnected in parallel, the switch movement controllingmeans being operatively connected to said resistances, the arms of thepotentiometers being connected to a source of current, the arm of one ofsaid potentiometers being movably connected with the motor shaft, meansresponsive to boiler conditions for'moving the arm of the otherpotentiometer.

10. A combustion control system for aboiler having a breeching andburning solid-fuel comprising, in combination, avmotor driven bloweroperatively connected to said boiler, a check draft 1 damper arranged inthe breeching, an electric circuit forsaid blower motor, a blower motorcircuit switch adapted to open and close said circuit, a control devicefor the motor circuit switch and the check draft damper comprising areversible motor having a shaft, said shaft being operatively connectedto the check draft damper and the motor circuit switch, an electriccircuit for the reversible motor, a movable switch arranged in thereversible motor circuit for controlling the direction of'rotation ofthe reversible motor, a pair of coils for controlling the movement ofthe movable switch, a pair of potentiometers having their resistancesconnected in parallel by the coils, the arms of one of saidpotentiometers being movably connected with the reversible motor shaft,means responsive to boiler conditions for moving the arm of the otherpotentiometer.

11. A combustion control system for a boiler having a breeching andburning solid fuel comprising, in combination, a motor driven bloweroperatively connected to said boiler, a check draft damper arranged inthe breeching, an electric circuit for said blower motor, a tiltablyoperated mercury tube switch arranged in said motor circuit and adaptedto open and close said circuit, a pivoted arm, means controlled by thepressure in said boiler for tilting said arm about its pivot, meansconnecting one end of the pivoted arm to the check draft damper andadapted to open said check draft damper upon tilting movement of saidpivoted arm in one direction and adapted to close said check draftdamper upon tilting movementinthe opposite direction, said pivoted armhaving the mercury tube switch arranged on the other end thereof to openand close the said 75 switch upon corresponding tilting of the saidpivoted arm, said pivoted arm, check draft damper, mercury tube, anddamper opening and closing means being arranged relatively to each otherso that upon the pivoted arm being tilted in one direction about itspivot, the check draft damper is closed before the mercury tube switehis closed and upon the pivoted arm being tilted in the other directionabout its pivot, the switch is opened before the check draft damper isopened.

CHARLES H. SMITH.

